It is known to provide active noise systems in motor vehicles, particularly hybrid electric vehicles, in which one or more speaker units are fitted. These speakers, in conjunction with various control means and methods, are used to provide noise waveforms, usually related to the ‘natural’ noise generated by the exhaust system. These noise waveforms may be used to ‘cancel out’ or minimise or suppress native exhaust notes, or may be used to enhance them. For example, external speaker systems are common in hybrid electric vehicles to generate vehicular noise when such vehicles are travelling under electric power in order to provide warning to pedestrians. Other arrangements involve enhancing the noise produced by the exhaust system where a sport mode is enabled and it is desirable to produce a particular noise profile. Yet further arrangements are configured to suppress exhaust noise in order to provide a quiet ‘luxury’ driving experience for drivers or passengers.
Active noise systems suffer if submerged in water. Such submersion may result from unexpected road flooding, in the case of a normal road vehicle, or as a result of intentional driving in the case of an ‘off-road’ or 4×4-type vehicle. In particular, when submerged the speakers suffer from attempting to work in the denser medium (water rather than air), which may result in physical damage as they attempt to vibrate the ‘working’ parts against the greater pressure of the surrounding medium.
Various methods have been suggested for protecting speaker systems against such damage, including physical protective methods such as waterproofing, pressure compensating surge tanks, speaker diaphragm stabilisers, and actuator snorkels. However, these all have implications for design and development, tooling, and piece price cost, as well as system complexity and packaging impact.
It is an aim of the invention to provide a solution that prevents damage to components whilst avoiding, or at least mitigating, the disadvantages of other prior art solutions.